This invention relates to permanent magnet dynamoelectric machines and more specifically to permanent magnet dynamoelectric machine rotors with the permanent magnets located in the interior of the rotor.
Electric generators of alternating current are sometimes excited or magnetized by means of permanent magnets because this leads to machines of simple, rugged construction having high efficiency and being free of slip rings or commutators.
It is important to obtain a sufficiently strong magnetic field in the air gap of the machine. However, it is often necessary to use permanent magnets whose optimum field strength is different from the field strength required in the air gap. Optimum field strength is the field strength in the magnet which maximizes the stored magnetic energy per unit volume in the magnet and which therefore leads to a design in which magnet volume, weight and cost are minimized.
In addition to obtaining optimum field strength, there is a problem of how to mechanically support the permanent magnets located in the interior of the rotor. The magnets, as well as the surrounding structures are subjected to various forces such as those arising from thermal expansion and rotation, and residual forces from the manufacturing process, such as distortions from welding.
In previous high peripheral speed permanent magnet rotor designs such as the one shown in Richter U.S. Pat. No. 4,117,360, issued Sept. 26, 1978 and assigned to the instant assignee, a composite shrink ring of magnetic and nonmagnetic pieces welded together is used to hold the magnets and the remaining rotor assembly. The pole pieces in the rotor assembly are solid pieces of magnetic material.
It is an object of the present invention to provide a rotor for a permanent magnet machine in which the magnets may be easily inserted.
It is a still further object of the present invention to provide a rotor for a permanent magnet machine in which high precision assembly is achieved with minimum thermal distortion from welding or brazing.
It is a still further object of the present invention to provide a two pole rotor for a permanent magnet machine which maximizes the stored magnetic energy, minimizing magnet volume, weight and cost.
It is another object of the present invention to provide a rotor with a central through-shaft.
It is yet another object of the present invention to provide a rotor with laminated pole pieces for a permanent magnet machine, which is suitable for use in large diameter high speed machines.